The present invention relates to chipper machines usable for removing portions of a workpiece such as a log, leaving behind a smooth flat surface, and in particular to apparatus and a method permitting such chipper machines to be operated more efficiently.
Chipper machines are large machines for removing and simultaneously comminuting parts of a workpiece, for example removing the rounded outer portions of a log to prepare a flat surface on one or more sides of the log as a reference for further cutting of the log into cants and boards. Typically a chipper machine comprises a horizontal mandrel supported in suitable radial and thrust bearings, with a chipper head hub fixedly attached to the mandrel. Arranged about the chipper head hub are several knives which extend generally radially and which comprise two legs joined by a curved portion.
Generally, a short leg of each chipper knife extends perpendicular to the axis of the mandrel, with its edge thus rotating in a plane as the chipper head is rotated with the mandrel. A long leg extends outwardly at an oblique angle from the short leg and away from the workpiece, so that the long leg edge describes a frustoconical surface as the chipper head is rotated.
As the chipper head is rotated the workpiece is fed past the chipper head in a direction perpendicular to the axis of rotation, so that the short legs of the blades cut a smooth flat surface on the workpiece, while the obliquely angled long legs of each chipper knife cut portions of the workpiece into small chips for convenient handling and further use. Such chipper machines are customarily used in conjunction with headrigs in saw mills, to slab logs and prepare cants for further sawing, and as edgers to cut waste wood from the edges of sawn boards in preparing dimension lumber.
In the past a chipper head hub has been fastened practically permanently to its mandrel, with knife holders fastened to the hub. Individual chipper knives are clamped adjustably in the knife holders and are individually removable for sharpening. An example of such individually removable knives and clamping holders is disclosed in Miller U.S. Pat. No. 3,777,793, the disclosure of which is hereby incorporated herein by reference.
When the knife edges of such a chipper machine begin to dull, it has previously been the practice to shut down the chipper machine and individually replace each chipper knife in its respective knife holder, adjusting the position of each chipper knife on the chipper head while the chipper head remains installed in the chipper machine. In fact, in most, if not all previous chipper machines, it is impossible to remove the chipper head from its arbor without first removing the mandrel from its bearings in the frame of the chipping machine, because of chip deflecting shrouding and work supporting anvils, which limit axial motion of the chipper head in the direction required to remove it from its arbor.
This procedure of individually replacing and adjusting resharpened chipper knives ordinarily requires about 20 to 30 minutes, and must be carried out in a dirty, usually noisy, environment which is not conducive to accuracy. This method of replacing dulled chipper knives is therefore subject to two serious deficiencies, both of which lead to unnecessary waste. First, the 20 to 30 minute period required for replacement of individual knives on the chipper head causes a significant reduction in the output of the chipper machine. Second, adjustment of the individual knives, even when done with the greatest care, under such circumstances is not as accurate as is desired. Any inaccuracy or variation in the location of the various knives of a single chipper head may result in wasteful unevenness on the plane surface of the log being slabbed or the lumber being edged by the chipper. This unevenness may require later planing of the wood product, an otherwise unnecessary step wasting time and wood. The inevitable dust and dirt present around a chipper machine which has been in operation often contributes to inaccuracy in positioning the replaced chipper knives, and additionally results in increased risk of damage to the newly resharpened chipper knife edges and injury to personnel replacing and adjusting chipper knives.
What is desired, then, is a chipper machine capable of being provided with resharpened knives in a significantly shorter amount of time, with a greater amount of accuracy than has previously been possible by replacing individual chipper knives on the chipper head. The chipper machine and the method of setting up the chipper knives of the chipper head according to the present invention greatly reduce the amount of time during which a chipper machine is out of operation because of dulled chipper knives, and simultaneously result in a more accurately cut plane surface on the workpiece.
The present invention provides a chipper machine having a chipper head which is quickly and easily removable from the arbor on which it is mounted for rotation. In the chipper machine of the present invention the arbor on which the chipper head is mounted is provided with a steep conical taper. For example, a reduction in arbor diameter of 31/2 inches per foot of arbor length permits the chipper head to be easily removed from the arbor, once a securing bolt is loosened. An attachment point is provided to permit the chipper head to be suspended, for example from a crane, during removal from the arbor. A portion of the housing of the chipper machine, such as a drop front anvil, which ordinarily may be used to support the workpiece being chipped, is removable from a position obstructing removal of the chipper head, so that the chipper head may be easily removed and replaced.
As a result, it is necessary only to move the anvil drop front, remove the securing bolt holding the chipper head onto the arbor, tap the hub of the chipper head to slide it from the mandrel while it is supported, as by a crane, and replace the dull chipper head with another complete chipper head, a procedure requiring considerably less time than the replacement of each individual chipper knife on the chipper head while it remains on the arbor.
While other industrial machines, for example, milling machines for cutting surfaces on metal workpieces, have included a rotary cutting head which was connected to a drive unit by means of a self-releasing steeply tapered conical connection, such milling heads include a conical stub shaft which fits within a conical socket, rather than having a conical socket in a hub which fits over a conical arbor. The method of repairing such milling machine cutter heads is different, in any case, since individual knives are not reground, adjusted, and replaced. Instead, individual cutter bits of such a milling machine cutter head are simply thrown away and replaced with new cutter bits.
Machines such as metalworking lathes utilize a nonbinding steeply tapered arbor to locate face plates or chucks on the drive shaft. Previously, however, there was no advantage seen in using this sort of a steeply tapered arbor for mounting a chipping head on a chipping machine.
A tapered arbor has, in fact, previously also been used in chipping machines, as illustrated in Hickman, U.S. Pat. No. 3,570,567, but no disclosure is made in this patent of a particularly steep taper of the arbor, nor any advantage to quick removal of the chipper head from the arbor.
The previously undiscovered advantage of such removability of a complete chipper head is that the chipper machine of the invention may thus be provided with a complete set of sharpened and aligned chipper knives in approximately five minutes of down time, as compared to the previously required 20 to 30 minutes of down time. Once a dulled chipper head has been removed from the chipper machine it may be removed to a shop where the individual chipper knives may be replaced with newly resharpened chipper knives which are first adjusted carefully, without the immediate pressure of time. The knives are finally dressed by a grinder to ensure that the plane-forming short leg portions of all of the knife edges rotate within a single plane, to provide a smooth planar surface on the workpiece. As a result of the final accurate grinder dressing of all of the chipper knives after installation in the chipper head, the chipper machine of the present invention is capable of providing a smoother plane surface on the work piece than is possible using the previously known method of individually replacing dulled chipper knives on a chipper head while it remains on the arbor of a chipper machine.
It is therefore a primary object of the present invention to provide a chipper machine in which dulled chipper knives may be replaced within a minimum of time during which use of the machine is prevented.
It is another important objective of the present invention to provide a chipper machine in which dulled chipper knives are replaced in precise alignment to provide a smooth plane surface on a work piece.
It is a further objective of the present invention to reduce the risk of damage to the edges of chipper knives during replacement of the chipper knives.
It is a principal feature of the present invention that the arbor and the mating socket in the hub of the chipper head of the chipper machine of the invention are provided with a taper which is sufficiently steep to permit quick release of the hub from the end of the mandrel.
It is another important feature of the present invention that it provides a movable anvil drop front to support a workpiece during operation of the chipper machine and still allow removal of the chipper head when the chipper knives have become dull.
It is a principal advantage of the present invention that it permits replacement of dulled chipper knives with a significantly shorter amount of time lost from chipper machine operation.
It is another important advantage of the present invention that it permits replacement of the individual chipper knives of a chipper head with greater precision than when the chipper head remains on the arbor of the chipper machine during installation of resharpened chipper knives.
It is yet further advantage of the present invention that it reduces the amount of material wasted during operation of the chipper machine, since it permits more precise adjustment of the position of the chipper head than was previously possible when chipper knives of the chipper head could not be so precisely located with respect to one another.
The foregoing and other objectives, features and advantages of the present invention will be more readily understood upon consideration of the following detailed description of the invention taken in conjunction with the accompanying drawings.